Gestational diabetes concerns “valid”

CONTINUING controversy surrounding the diagnostic thresholds for gestational diabetes is presenting problems for GPs, says a leading endocrinologist.
    
Professor David McIntyre, director of endocrinology and obstetric medicine at Brisbane’s Mater Health Services, said there was “fairly broad consensus and some vocal dissent” about the new lower thresholds for gestational diabetes (GDM).

“That does make it exceedingly difficult for GPs. I know at the moment there are laboratories putting [both the] old criteria and the new set of criteria on their reports, which means that a woman can both have GDM and not have GDM … so it’s getting a bit ridiculous.”

Professor McIntyre was commenting on two “For debate” articles published in the MJA — one questioning the statistical basis of the new risk threshold and another suggesting that the implementation of new treatment targets was premature. (1), (2)

The articles follow the Australian Diabetes in Pregnancy Society’s (ADIPS) adoption of the WHO diagnostic criteria for gestational diabetes, which is in line with the International Association of Diabetes and Pregnancy Study Groups’ threshold consensus. (3)

Writing in the MJA, Associate Professor Michael d’Emden, director of endocrinology and diabetes at Royal Brisbane Women’s Hospital, suggested some minor modifications to the criteria could more accurately identify patients whose babies were large for gestational age.

In the other MJA article, Dr Dev Kevat of Monash University’s school of public health, and coauthors, said lowering the treatment targets for gestational diabetes to 5.0 mmol/L fasting, 7.4 mmol/L at 1 hour and 6.7 mmol/L at 2 hours after meals was premature.

Dr Kevat said although ADIPS guidelines had described these lower targets as “suggestions”, many doctors would be looking to these targets for direction. “While there may be benefits, lowering treatment targets may cause a number of harms including increased risk of hypoglycaemia in pregnant women, greater medicolegal risk for health practitioners, and heavier economic costs for the health system”, he wrote.

Professor McIntyre, a council member of ADIPS and a former president, said the MJA paper had “over-interpreted” the aim of the treatment targets, which ADIPS had acknowledged required further research.

“Most people would say that exactly which numbers one should aim for in treatment needs to be tempered by the individual woman and her baby and the clinical situation”, he told MJA InSight.

Professor McIntyre said concerns about overtreatment were valid. “You don’t want to be overtreating people just to try to achieve a notional set of numbers. But on the other hand … in our clinic we have been treating people to an overall fasting glucose target of 5 mmol/L for several years without ever producing an episode of severe hypoglycaemia”, he said.

Professor Stephen Colagiuri, professor of metabolic health at the University of Sydney and a co-chair of the 2011 WHO committee that recommended the adoption of the new criteria, also said the points raised in the MJA about treatment targets were valid. (4)

“They are guides, but as pointed out … there may be medicolegal issues if you don’t aim for those and something happens, as does unfortunately from time to time, with the outcome of a pregnancy. So this is a very controversial area … and the evidence to support [treatment targets] is not as strong as those for the diagnostic criteria.”

Professor Colagiuri said there was broad agreement on the new diagnostic criteria regarding the recommendation to use the 75 g oral glucose tolerance test to assess glucose tolerance status. Those women meeting the criteria (blood sugar level >= 7.0 mmol/L fasting and/or >=11.1 mmol/L at 2 hours) for diabetes should be diagnosed with diabetes rather than being labelled as having gestational diabetes. GDM is now applied to women with levels below diabetes but above “normal”. 

However, he said the decision to lower the fasting glucose level to 5.1 mmol/L for a diagnosis of GDM had proved to be controversial.

“WHO recognises that the evidence is low, but [adopted these criteria] for the sake of international consensus so that we can move forward and try to sort out these controversies”, Professor Colagiuri said.

“[The d’Emden article] makes a good point … there are some issues with the outcomes that have been selected to determine these new criteria. There was debate [at the WHO] as to whether to adopt the 1.75 times risk of outcomes or two times risk, but nevertheless the group decided to go with the 1.75 times.”

Earlier this year, the Royal Australian College of General Practitioners (RACGP) decided not to endorse the ADIPS recommendations, preferring to support the existing recommendations until further evidence became available. (5)

Professor Colagiuri said the RACGP’s decision not to endorse the new diagnostic criteria was “unfortunate”.

“We are dealing with a continuous variable — there is no magic point at which you can say somebody is normal or abnormal”, he said.

“It may be in 5 years’ time we decide that these criteria are still as good as anything … or maybe they need to be tweaked.”

1. MJA 2014; 201: 209-211
2. MJA 2014; 201: 204-207
3. ADIPS 2014: Consensus guidelines for the testing and diagnosis of gestational diabetes mellitus in Australia
4. WHO 2013: Diagnostic criteria and classification of hyperglycaemia first detected in pregnancy
5. RACGP: General practice management of type 2 diabetes 2014–2015

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